Disposal of separated water from the vapor condenser and distiller sections of modern dry cleaning machines is a present problem without heretofore an easy answer. Some dry cleaners pour this water which condenses from the dry cleaning machine out the back door of their plant into the ground. Although there is no visual indication of dry cleaning solvents such as PERC (Perchloroethylene), this condensate water can still contain 150-2,000 ppm dissolved PERC solvent. If carry over or other malfunction of the dry cleaning machine has occurred, then the water may be even more potent.
Pouring this water on the ground will result in PERC contamination especially where there this disposal technique is continued over long periods of time. A paved parking lot or paved driveway is not a secure barrier to PERC solvent. It has been documented that PERC solvent will penetrate asphalt in less than 24 hours. Once in the soil the PERC will continue to penetrate the soil until it reaches bedrock. Most of the time, ground water is encountered on top of the bedrock. PERC then lays in the bottom of the ground water layer and slowly dissipates making the ground water unfit for human consumption. Applicant believes that this ground water contamination by PERC is much more of a threat than inhalation of PERC vapor.
Some dry cleaners trying to dispose of the water PERC mixture have routed the PERC mixture into the reservoir tank of the water cooler/heat exchanger (roof cooling tower). While this practice seems acceptable, the long term application of PERC solvent into the cooling water in high humidity and hot climates may cause accelerated corrosion of the cooling tower materials.
Pouring the water PERC mixture into a Hazardous Waste Containers is legal. However, many haulers have objected to adding water to the distillate residue as it makes the recovery distillation cycle more time consuming and less economical, and thus this route is very expensive if available at all.
Pouring the separated water into the drain and thus to a sewer treatment plant, is certainly better than pouring the water on the ground. However, many treatment plant operators, are issuing many new and stringent regulations on their sludge, discharge and disposal. Sewer treatment plant operators are also becoming more aware of where the solvents are coming from, and this will mean eventually that even small businesses will be regulated and monitored. In a small number of cases, broken sewer lines have caused problems for dry cleaners that have followed disposal of separator water into the municipal sewer treatment plan.
Pouring the separator water into a drain that leads to a septic system, or to a storm drain is unacceptable and should be discontinued immediately. The dry cleaner who practices this disposal technique will risk business ending expense, clean up expenses, as well as possible third-party liable. Further, a contaminated septic system may make the property and the business unsalable.
Heretofore, two alternatives have been used in the modern dry cleaning plant. One is evaporation, the other is constant flow pretreatment. In evaporation, the separator water is collected, vaporized, and exhausted, with a mist of water vapor going into the atmosphere. This has been used for many years by dry cleaners using homemade devices. When PERC saturated water is vaporized, the resulting steam or mist occupies significantly more space. The concentration of PERC in the mist or vapor is substantially less than in water. Therefore, the mist usually has less odor. While there are advantages of evaporation disposal, e.g. no liquid discharge to the sewer, and usually no carbon filters. The disadvantages are many. These include the operating cost of the steam and/or electricity required to vaporize the separator water, required air emission permits as may be needed in several jurisdictions, cost of maintenance of the heat exchanger heating element which is expensive, corrosion of the coils, and film which develops on the coils which reduces efficiency and must be cleaned. Also, capacity is usually low because of poor heat transfer, and noxious odors may be created in the plant. Finally, on electric models, the high power requirements may require separate circuits, additional line protection, ground faults, etc.
The constant flow water pretreatment approach has several possibilities. One is pretreatment of the water to minimize PERC content and monitor the levels of PERC being routed to the sewer treatment plant. Waste water pretreatment is a common technique used in other industries with great success. PERC may be easily removed from the water at relatively low concentrations found in separated water using the following techniques. Another is installation of supplemental mechanical separator, like the separator installed in the dry cleaning machine, to remove the PERC solvent. Several of the new dry cleaning machines displayed recently have such second separators. Several of these second separators have outlets which permit an operator to drain the machine to drain PERC liquid back to the distillation unit and water to the drain. These units are believed to have several shortcomings in that, depending upon the temperature and elevation, water can contain 400 plus ppm PERC without showing it. Another alternative is a liquid phase carbon, to remove solvents from water. The water is placed in contact with carbon, and under the right circumstances, of flow and distribution, the carbon will remove PERC from the water. Carbon used in this application may last long periods of time, but will eventually require legal disposal. Still another approach is air stripping, which has been used by environmental companies to treat ground water and remove halogenated solvents for several years. Because of its relative volatility, PERC can be stripped from separated water with the right application of air, temperature and distribution.
Although there are advantages to constant flow water pretreatment, and they include that steam and high energy sources are not required, maintenance is low, discharge odors are eliminated, and capacities are higher than evaporation; there are important disadvantages, of high cost, treated discharge into sewer, that disposal is still required, and a risk of not collecting all of the PERC, and thus releasing it.
Pretreatment is obviously a better alternative to evaporation disposal in locations where emissions are closely monitored, such as under apartments, or in malls. When state and local agencies respond to odor complaints, any and all discharges to the atmosphere become suspect. Businesses, such as large dry cleaners, laundries and linen services are presently using pretreatment for other waste water contaminants. Meanwhile, state agencies and sewer plant authorities have established programs for the registration and the regulation for pretreatment waste water. These regulatory systems have been in place for some time, are growing and are sometimes bureaucratic. Evaporation is obviously the better alternative in states and jurisdictions where sewer discharges are sensitive, and in addition, dry cleaning plants operating on septic systems which should avoid any and all industrial discharge into the septic system.